1. Field of the Invention
The present invention relates to manufacturing techniques of display devices, and in particular to active-matrix type array substrates for electroluminescence display devices.
2. Description of the Related Art
New generation of flat panel devices, such as organic light emitting display (OLED) devices of electroluminescent displays have advantages of self-luminescence, a thin profile, being light weight, and having high luminance efficiency. In accordance with driving methods, an OLED device can be classified as an active matrix type or a passive matrix type OLED device.
Nevertheless, to enhance image resolution of the OLED devices, luminance of display pixels in the OLED device can be further improved.
In FIG. 1, a conventional electroluminescent (EL) device disclosed in Japanese laid-open patent application No. 2003-257662 is illustrated. The EL device includes components such as an insulating substrate 10, a gate electrode 11, a gate insulating layer 12, an active layer 13 (including a channel region 13c, a drain region 13d and a source region 13s), a stop layer 14, an interlayer insulating layer 15, a drain electrode 16, a planar insulating layer 17, an anode 22, a hole transport layer 23, a light emitting layer 24, an electron transport layer 25, and a cathode 26.
Since the planar insulating layer 17 is formed with a rugged top surface, the anode 22, the hole transport layer 23, the light emitting layer 24, the electron transport layer 25, and the cathode 26 are conformably formed over the planar insulating layer 17. Thus, the above-mentioned layers formed over the planar insulating layer 17 also have rugged top surfaces. Thus, the light emitting area S1 of a light emitting element formed of the anode 22, the hole transport layer 23, the light emitting layer 24, the electron transport layer 25, and the cathode 26 all have increased rugged top surfaces, improving luminance.
Nevertheless, the anode 22 illustrated in FIG. 1 functions as a reflection layer, and the hole transport layer 23 encapsulating the anode 22 may cause negative battery effects and corrosion at edges of the anode 22. In addition, since the planar insulating layer 17 is formed with the rugged top surface, film delamination may occur between the anode 22 and the planar insulating layer 17 formed thereon. The above two undesired phenomena decrease reliability of the light emitting element.
In FIG. 2, a conventional OLED device according to a reference entitled “A 20.8-inch WXGA Full Color AMOLED Display by integrating Scattering Reflector with Micro-Bumps” of SID 07 DIGGEST, p 173-176, is illustrated.
As shown in FIG. 2, the OLED device includes a cap glass 66, a substrate 50 and sealant 68 for substantially defining a space for disposing a display pixel. The display pixel is substantially formed of elements such as a thin film transistor 52, micro-bumps 54, a reflection layer 56, a planar layer 58, an anode 60, an emission layer 62 and a cathode 64 wherein the anode 60, emission layer 62 and cathode 64 form a light emitting element and thus emits light 70 during operation thereof. Scattered light 72 is also provided from the reflection layer 56 and light extraction efficiency of the display pixel can thus be improved.
However, since the reflection layer 56 is formed with a rugged top surface, an additional process is needed to form the planar layer 58 on the reflection layer 56 for the convenience of sequentially formed elements fabrication. In addition, since the layers for forming the light emitting element are planarization films, a light emitting region therein is relative small, thus hindering light extraction efficiency and light luminance thereof.